v1.18: RPC: rewards, return error if epoch_boundary_block is a lie (backport of #2758) (#2781)

* RPC: rewards, return error if epoch_boundary_block is a lie (#2758)

* Return error if epoch_boundary_block is not actually the epoch boundary block

* Update rpc-client-api/src/custom_error.rs

Co-authored-by: Trent Nelson <[email protected]>

---------

Co-authored-by: Trent Nelson <[email protected]>
(cherry picked from commit 9a4b094)

# Conflicts:
#	rpc-client-api/src/custom_error.rs
#	rpc/src/rpc.rs

* Fix conflicts

---------

Co-authored-by: Tyera <[email protected]>

Author: 2 people

rpc-client-api/src/custom_error.rs

@@ -24,6 +24,8 @@ pub const JSON_RPC_SERVER_ERROR_TRANSACTION_SIGNATURE_LEN_MISMATCH: i64 = -32013
 pub const JSON_RPC_SERVER_ERROR_BLOCK_STATUS_NOT_AVAILABLE_YET: i64 = -32014;
 pub const JSON_RPC_SERVER_ERROR_UNSUPPORTED_TRANSACTION_VERSION: i64 = -32015;
 pub const JSON_RPC_SERVER_ERROR_MIN_CONTEXT_SLOT_NOT_REACHED: i64 = -32016;
+const _RESERVED_FOR_V2_0_ERROR: i64 = -32017;
+pub const JSON_RPC_SERVER_ERROR_SLOT_NOT_EPOCH_BOUNDARY: i64 = -32018;
 
 #[derive(Error, Debug)]
 pub enum RpcCustomError {
@@ -65,6 +67,8 @@ pub enum RpcCustomError {
     UnsupportedTransactionVersion(u8),
     #[error("MinContextSlotNotReached")]
     MinContextSlotNotReached { context_slot: Slot },
+    #[error("SlotNotEpochBoundary")]
+    SlotNotEpochBoundary { slot: Slot },
 }
 
 #[derive(Debug, Serialize, Deserialize)]
@@ -206,6 +210,14 @@ impl From<RpcCustomError> for Error {
                     context_slot,
                 })),
             },
+            RpcCustomError::SlotNotEpochBoundary { slot } => Self {
+                code: ErrorCode::ServerError(JSON_RPC_SERVER_ERROR_SLOT_NOT_EPOCH_BOUNDARY),
+                message: format!(
+                    "Rewards cannot be found because slot {slot} is not the epoch boundary. This \
+                     may be due to gap in the queried node's local ledger or long-term storage"
+                ),
+                data: None,
+            },
         }
     }
 }

rpc/src/rpc.rs

@@ -575,6 +575,20 @@ impl JsonRpcRequestProcessor {
             .into());
         };
 
+        // If there is a gap in blockstore or long-term historical storage that
+        // includes the epoch boundary, the `get_blocks_with_limit()` call above
+        // will return the slot of the block at the end of that gap, not a
+        // legitimate epoch-boundary block. Therefore, verify that the parent of
+        // `epoch_boundary_block` occurred before the `first_slot_in_epoch`. If
+        // it didn't, return an error; it will be impossible to locate
+        // rewards properly.
+        if first_confirmed_block.parent_slot >= first_slot_in_epoch {
+            return Err(RpcCustomError::SlotNotEpochBoundary {
+                slot: first_confirmed_block_in_epoch,
+            }
+            .into());
+        }
+
         let addresses: Vec<String> = addresses
             .into_iter()
             .map(|pubkey| pubkey.to_string())